Low Pass Filtering

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Low Pass Filtering

A low pass filter is the basis for most smoothing methods. An image is smoothed by decreasing the disparity between pixel values by averaging nearby pixels. Using a low pass filter tends to retain the low frequency information within an image while reducing the high frequency information. An example of a low pass filter is an array of ones divided by the number of elements within the kernel, such as the following 3 by 3 kernel:

The above array is just an example of one possible kernel for a low pass filter. Other filters may include more weighting for the center point, or have different smoothing in each dimension.

The following example uses the CONVOL function to smooth a whirlpool galaxy M51 image. This example data is available in the examples/data directory of your IDL installation. The code shown below creates the following images:

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